Radiation detecting apparatus and method of driving the same

ABSTRACT

A radiation detecting apparatus including a plurality of pixels, each pixel including a conversion element configured to convert radiation into an electric signal, a resetting element configured to reset the conversion element by applying a predetermined voltage to the conversion element, and a signal transfer element connected to the conversion element. The signal transfer element and the resetting element are connected to the same electrode of the conversion element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiation detecting apparatus fordetecting radiation such as an X-ray or a γ-ray, and more particularly,to a radiation detecting apparatus suitable for use in a medical imagediagnosis apparatus, a non-destructive examination apparatus, ananalysis apparatus using radiation, and the like.

2. Description of the Related Art

Imaging methods used in medical diagnostic imaging can be classifiedinto general imaging for obtaining a still image and radiographicimaging for obtaining a moving image. Suitable imaging methods andapparatuses may be selected as required.

One known method of general imaging for obtaining a still image includesexposing a film of a screen-film system (hereinafter referred to as anS/F system) comprised of a combination of a fluorescent plate and afilm, developing the film, and then fixing the resultant image. Anotherknown method is computed radiography (CR) in which a radiogram is firstrecorded in the form of a latent image on a photostimulable phosphorplate, and then the photostimulable phosphor plate is scanned with alaser beam and output optical information is read using a sensor.

However, a problem in these methods is that they require complicatedwork flow to obtain a radiographic image. Another problem is that adigital image can only be obtained indirectly via processing, whichrequires a long time. That is, a digital image cannot be obtained inreal time. Thus, there is less merit in employing the conventionalmethods described above, compared with digital imaging methods such ascomputer tomograph (CT) or magnetic resonance imaging (MRI) used inmedical diagnosis.

On the other hand, in the radiography for obtaining a moving image, oneknown method is to use an electron tube as an image intensifier (II).However, this method needs a large-scale apparatus including theelectron tube. Also, the field of view or the detection area istypically not large enough to meet the requirements in medicaldiagnostic imaging. Furthermore, an obtained moving image includes alarge amount of crosstalk arising from a specific structure of theapparatus, and it is desirable to reduce crosstalk to obtain a clearerimage.

On the other hand, recent advances in the liquid crystal Thin FilmTransistor (TFT) technology and information infrastructure have made itpossible to realize a flat panel detector (FPD) composed of a sensorarray and a fluorescent substance for converting radiation into visiblelight, wherein the sensor array is made up of optical-to-electricalconverters using non-single silicon crystal such as amorphous silicon(a-Si) and switching TFTs. This technique is expected to make itpossible to realize large-area imaging in a fully digital form.

The FPD is capable of reading a radiographic image and displaying theimage on a display in real time. Another advantage is that a digitalimage can be obtained directly, and data can be easily stored,processed, and transferred. Although characteristics such as sensitivitydepend on imaging conditions, the characteristics are generally similarto or better than the characteristics obtained in the conventional S/For CR imaging techniques.

FIG. 13 shows a known equivalent circuit of an FPD. In FIG. 13,reference numeral 101 denotes a photoelectric conversion element, 102denotes a transfer TFT, 103 denotes a driving line for driving thetransfer TFT, 104 denotes a signal line, 105 denotes a bias line, 106denotes a signal processing circuit, 107 denotes a TFT driving circuit,and 108 denotes an A/D converter.

If radiation is incident on the photoelectric conversion element 101,the incident radiation is converted in wavelength into visible light bya fluorescent substance (not shown). The resultant converted light isthen converted to an electric charge by the conversion element 101 andstored in the conversion element 101. Thereafter, the TFT drivingcircuit 107 drives the transfer TFT 102 via the TFT driving line so asto transfer the stored charge to the signal processing circuit 106 viathe signal line 104. The charge is processed by the signal processingcircuit 106 and then converted by the A/D converter 108 from analog forminto digital form. The resultant digital signal is output.

An example of the device structure widely used for the FPD has beendescribed above. As for the optical-to-electrical converter, variousdevice structures such as a p-type layer/intrinsic layer/n-type layerphotodiode (PIN PD) and a MIS-type optical-to-electrical convertersimilar to that employed in the present invention have been proposed.

FIG. 14 is a plan view showing one pixel in which a MIS-typeoptical-to-electrical converter is used. In FIG. 14, reference numeral201 denotes a MIS-type optical-to-electrical converter, 202 denotes atransfer TFT, 203 denotes a driving line for driving the transfer TFT,204 denotes a signal line, 205 denotes a sensor bias line, 211 denotes agate electrode of a transfer TFT, 212 denotes source and drainelectrodes (hereinafter, referred to simply as SD electrodes) of thetransfer TFT, and 213 denotes a contact hole.

FIG. 15 is a cross-sectional view of one pixel including various devicesshown in FIG. 14. In FIG. 15, reference numeral 301 denotes a glasssubstrate, 302 denotes a driving line for driving the transfer TFT, 303denotes a lower electrode of the MIS-type optical-to-electricalconverter, 304 denotes a gate electrode of the transfer TFT, 305 denotesa gate insulating film, 306 denotes an intrinsic a-Si film, 307 denotesa hole blocking layer, 308 denotes a bias line, 309 denotes SDelectrodes of the transfer TFT, 310 denotes a signal line, 320 denotes aprotective film, 321 denotes an organic resin layer, and 322 denotes afluorescent substance layer.

As can be seen from FIGS. 14 and 15, the MIS-type optical-to-electricalconverter and the transfer TFT have the same layer structure, and thusthey can be produced using a simple production method which allows ahigh production yield and low production cost. Furthermore, the FPDconstructed in the above-described manner performs well in variousaspects, including sensitivity, and it has come to be used in generalimaging applications instead of conventional S/F method and CR methodapparatuses.

However, although the FPD has the advantage that a fully digitallarge-area image can be obtained and the FPD has come to be used widelyin general imaging, the FPD according to the conventional technologydoes not have a high enough reading speed needed in radiographicimaging.

FIG. 16 shows an equivalent circuit of a one-bit portion of an FPD usingMIS-type optical-to-electrical converters. In FIG. 16, reference symbolC1 denotes total equivalent capacitance of the MIS-typeoptical-to-electrical converter, C2 denotes parasitic capacitanceassociated with the signal line, Vs denotes a sensor bias voltage, Vrdenotes a sensor reset voltage, SW1 denotes a switch for selecting Vs orVr applied to the MIS-type optical-to-electrical converter, SW2 denotesa switch for turning on/off the transfer TFT, SW3 denotes a switch forresetting the signal line, and Vout denotes an output voltage.

When the switch SW1 is at the Vs position, the voltage Vs is applied asa bias voltage to the MIS-type optical-to-electrical converter such thatthe semiconductor layer of the MIS-type optical-to-electrical converteris depleted. In this state, if light converted via the fluorescentsubstance is incident on the semiconductor layer, a positive chargeblocked by the hole blocking layer is accumulated into the a-Si layer,and a voltage difference Vt occurs. Thereafter, when the on-voltage isapplied to the transfer TFT via the SW2, the voltage Vout is output. Theoutput voltage Vout is read by a reading circuit (not shown). Afterthat, the signal line is reset by the switch SW3, and reading isperformed sequentially.

By sequentially turning on transfer TFTs on a line-by-line basisaccording to the driving scheme described above, one entire frame isread. Thereafter, the MIS-type optical-to-electrical converter is resetby applying the reset voltage Vr to it via the SW1, and the bias voltageVs is again applied thereby causing the charge accumulation to start inthe reading operation.

For example, when the FPD has pixels with a size of 160 μm disposed in apixel area with a size of 43 cm×43 cm, the total equivalent capacitanceC1 of the MIS-type optical-to-electrical converter is about 1 pf and theparasitic capacitance C2 is about 50 pf. In such an FPD, when the chargeis transferred, about 2% of the charge remains in the capacitor C1without being transferred because of the charge sharing effect. Thus, toobtain a high-quality image, it is necessary to perform the resettingoperation described above.

More specifically, the resetting operation needs ten msec or a few tenmsec for each frame, depending on the resetting condition. Therefore,when it is desired to take a radiographic image at a rate of 30 framesper second (FPS) or at a higher rate, it is required to perform readingand resetting on all lines of one frame within a period of 33 msec (30FPS).

FIG. 17 is a diagram showing a conventional method of driving an FPD. InFIG. 17, reference symbol T1 denotes a period of time needed to read oneline, T2 denotes a period of time needed to read all lines, T3 denotes areset time, and T denotes a period of time needed to perform the entireprocess on one frame. In the case in which it takes 33 msec to performthe entire process on one frame as described above, if the reset time T3is equal to 15 msec, then T2 becomes 18 msec. Therefore, if there are1500 lines to be read, the period of time T1 available for reading oneline becomes 12 μsec. If a radiation exposure time, that is, a sensoraccumulation time is taken into account, the reading period T1 isfurther limited. Thus, it becomes necessary to increase the transfercapacity of the transfer TFT. However, to increase in the transfercapacity of the transfer TFT, it is necessary to increase the size ofthe transfer TFT at the cost of the aperture ratio, which causes variousproblems such as a reduction in sensitivity, degradation in imagequality, and an increase in the amount of radiation necessary togenerate an image.

That is, a trade-off is needed between the high image quality and thehigh speed at which the FPD is driven to obtain a moving image. In otherwords, at present, it is impossible to achieve a high-speed moving imagehaving high quality.

In view of the above, U.S. Pat. No. 5,869,837 to Huang discloses aradiographic image forming system including resetting means forperiodically resetting capacitively coupled radiation detection means.However, in this radiographic image forming system, a protective film ofa reading switch is also used as an insulating film of a reset switch.Also the connection position of the reset switch disclosed does notnecessarily allow the radiation detection means to be fully reset. Thusthere is some room for improvement in the layer structure and inresetting of the radiation detection means.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided aradiation detecting apparatus including a plurality of pixels, eachpixel including a conversion element configured to convert radiationinto an electric signal, a resetting element configured to reset theconversion element by applying a predetermined voltage to the conversionelement, and a signal transfer element connected to the conversionelement. The signal transfer element and the resetting element areconnected to the same electrode of the conversion element.

In this radiation detecting apparatus, it is desirable to form theconversion element on the signal transfer element and also on theresetting element to further improve the aperture ratio.

According to another aspect of the present invention, there is provideda method of driving a radiation detecting apparatus including an arrayof pixels each including detection means for detecting radiation,transfer means for transferring a detected signal, and resetting meansfor resetting the signal by applying a voltage to the detection means,the method comprising performing a signal transfer operation of pixelsin a specific row in a period of time in which a signal resettingoperation is being performed for a row the signal transfer operation forwhich has been completed before starting the signal transfer operationfor the specific row.

Further objects, features and advantages of the present invention willbecome apparent from the following description of the preferredembodiments with refer to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing an equivalent circuit of an X-raydetecting apparatus having a 3×3 matrix structure, according to a firstembodiment.

FIG. 2 is a circuit diagram showing an equivalent circuit of an X-raydetecting apparatus having a 3×1 matrix structure.

FIG. 3 is a diagram showing a method of driving the X-ray detectingapparatus having a 3×3 matrix according to the first embodiment.

FIG. 4 is a plan view showing one pixel of the X-ray detecting apparatushaving a 3×3 matrix according to the first embodiment.

FIGS. 5A and 5B are plan views showing a method of producing the X-raydetecting apparatus according to the first embodiment, wherein steps ina production process are shown.

FIGS. 6A and 6B are plan views showing a method of producing the X-raydetecting apparatus according to the first embodiment, wherein stepsfollowing those shown in FIG. 5 are shown.

FIG. 7 is a circuit diagram showing an equivalent circuit of an X-raydetecting apparatus having a 3×3 matrix structure, according to a secondembodiment.

FIG. 8 is a circuit diagram showing an equivalent circuit of an X-raydetecting apparatus having a 3×1 matrix structure.

FIG. 9 is a diagram showing a method of driving the X-ray detectingapparatus having a 3×3 matrix according to the second embodiment.

FIG. 10 is a plan view showing one pixel of the X-ray detectingapparatus having a 3×3 matrix according to the second embodiment.

FIG. 11 is a circuit diagram showing an equivalent circuit of an X-raydetecting apparatus having a 3×3 matrix structure, according to a thirdembodiment.

FIG. 12 is a cross-sectional view showing a pixel and nearby portions ofthe X-ray detecting apparatus according to the third embodiment.

FIG. 13 is a circuit diagram showing an equivalent circuit of aconventional X-ray detecting apparatus in the form of an FPD.

FIG. 14 is a plan view of one pixel including a MIS-typeoptical-to-electrical converter of a conventional X-ray detectingapparatus.

FIG. 15 is a cross-sectional view of one pixel including various devicesshown in FIG. 14.

FIG. 16 is a circuit diagram showing an equivalent circuit of a one-bitportion of a conventional X-ray detecting apparatus using MIS-typeoptical-to-electrical converters.

FIG. 17 is a diagram showing a method of driving the FPD type X-raydetecting apparatus according to the conventional technique.

FIG. 18 is a cross-sectional view taken along line A-A of FIG. 4.

FIG. 19 is a cross-sectional view taken along line B-B of FIG. 4.

FIG. 20 is a cross-sectional view of a radiation detecting apparatusaccording to a fourth embodiment.

DECRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described infurther detail below with reference to the accompanying drawings.

First Embodiment

In this first embodiment, of the present invention, there is disclosedan FPD-type X-ray detecting apparatus using a MIS-typeoptical-to-electrical converter as a sensor portion.

FIG. 1 is a circuit diagram showing an equivalent circuit of an X-raydetecting apparatus having a 3×3 matrix structure according to thepresent embodiment. Although the X-ray detecting apparatus has the 3×3matrix structure by way of example, the matrix structure may includegreater numbers of rows and columns.

In FIG. 1, reference numeral 11 denotes an individual MIS-typephotoelectric conversion element, 12 denotes a first thin-filmtransistor (switching element) serving as a transfer TFT, 13 denotes atransfer TFT driving line 14 denotes a signal line, 15 denote a biasline, 16 denotes a signal processing circuit, 17 denotes a TFT drivingcircuit, 18 denotes an A/D converter, 19 denotes a second switchingelement serving as a reset TFT, 20 denotes a driving line for drivingthe reset TFT, and 21 denotes a resetting line.

A radiation detection part is formed of the photoelectric conversionelement 11 and a wavelength conversion element, described later, forconverting the wavelength of radiation. As described above, the X-raydetecting apparatus according to the present embodiment includesswitching means for switching an electric signal output from theMIS-type optical-to-electrical converter 11, wherein one of theswitching means is the TFT12 serving as a transfer element fortransferring the electric signal, and the other one is the TFT 19serving as a resetting element for resetting the electric signal byapplying a constant voltage to the MIS-type optical-to-electricalconverter 11.

Incident X-ray radiation is converted into visible light by a wavelengthconversion element such as a cesium iodide (CsI) or Gd₂O₂S (GadoliniumOxySulphide) (GOS), and the resultant visible light is incident on theMIS-type photoelectric conversion element 11. The incident light isconverted into an electric charge by the MIS-type photoelectricconversion element 11, and the resultant electric charge is stored inthe MIS-type photoelectric conversion element 11. Thereafter, thetransfer TFT 12 is turned on to read the stored electric charge. Thereset TFT 19 is then turned on to reset the signal charge stored in theMIS-type photoelectric conversion element. In the alternative, theelectric charge may also be stored in an additionally provided storagecapacitor.

FIG. 2 is a circuit diagram showing an equivalent circuit of an X-raydetecting apparatus having a 3×1 matrix structure. In this figure,similar parts to those in FIG. 1 are denoted by similar referencenumerals. When an on-voltage is applied to a transfer TFT via a nodeVgt(1), a signal is output via a line Sig. If an on-voltage is appliedto a reset TFT via a node Vgr(1), a sensor is reset. Similarly, when anon-voltage is applied to a transfer TFT via a node vg(2), a signal isoutput via the line Sig. Thereafter, an on-voltage is applied to a resetTFT via a node Vgr(2) to reset a sensor. By sequentially applyingVgt(1), Vgr(1), Vgt(2), Vgr(2), . . . , Vgt(4), Vgr(4) shown in FIG. 2in a similar manner as described above, it is possible to performreading of a moving image and resetting.

FIG. 3 is a diagram showing a method of driving the X-ray detectingapparatus according to the present embodiment. In FIG. 3, referencesymbol S1 denotes a period of time needed to read one line, S2 denotes aperiod of time needed to reset one line, S4 denotes a period of timeneeded to accumulate an electric charge into a sensor, and S denotes aperiod of time needed to perform the entire process on one frame.

In the present embodiment, unlike the conventional method in whichsequential reading and resetting and exposure to radiation for allpixels are performed repeatedly, reading, resetting, and storing areperformed on a line-by-line basis, and thus the total driving time issubstantially equal to the sum of reading times. That is, when readingand transferring of signals from pixels in one line are being performed,resetting of already-read pixels in a previous line is performed. Thismakes it possible to drive the X-ray detecting apparatus at a highdriving rate of 30 FPS or higher to obtain a moving image withoutcausing degradation in image quality.

FIG. 4 is a plan view showing one pixel of the X-ray detecting apparatusaccording to the present embodiment. In FIG. 4, similar parts to thosein FIG. 1 are denoted by similar reference numerals. In FIG. 4, thetransfer TFT 12 and the reset TFT 19 are disposed in diagonally oppositecorners of the pixel in order to achieve an optimum layout including thedriving line and the signal line. FIG. 18 is a cross-sectional viewtaken along line A-A of FIG. 4, and FIG. 19 is a cross-sectional viewtaken along line B-B of FIG. 4. In those figures, similar functionalparts to those in FIG. 1 are denoted by similar reference numerals. Ascan be seen from FIGS. 18 and 19, the lower electrode of theoptical-to-electrical converter (303 shown in FIG. 5A), the gateelectrode of the signal transfer TFT, and the gate electrode of thereset TFT are connected together, that is, the signal transfer TFT andthe reset TFT are both connected to the same electrode of theoptical-to-electrical converter, thereby making it possible to achievehigh-performance resetting operation.

Referring to FIGS. 5 and 6, a method of producing the X-ray detectingapparatus according to the present invention is described below. First,as shown in FIG. 5A, the gate electrode and the driving line 13 of thetransfer TFT, the lower electrode 303 of the MIS-typeoptical-to-electrical converter, and the driving interconnection line 20of the reset TFT are formed. The gate electrode may be formed by firstdepositing a thin chromium film with a thickness of about 150 nm bymeans of sputtering and then patterning it by means of photolithography.

Thereafter, the SiN gate insulating film, the a-Si film, and the n⁺-filmof the TFT and the MIS-type optical-to-electrical converter are formedto thickness of about 300 nm, 600 nm, and 100 nm, respectively, using aplasma CVD apparatus.

Thereafter, as shown in FIG. 5B, a contact hole 213 is formed by meansof photolithography using Reactive Ion Etching (RIE) or Chemical DryEtching (CDE).

Furthermore, as shown in FIG. 6A, SD electrodes 24 and 25 of thetransfer TFT and the reset TFT, the signal line 14, the bias line 15,and the reset line 21 are formed by first depositing a thin aluminumfilm (with a thickness of about 1 μm) by means of sputtering and thenpatterning the thin aluminum film by means of photolithography.

Thereafter, the n⁺-film is removed selectively from the gap regions ofthe transfer TFT and the reset TFT by means of RIE.

Furthermore, as shown in FIG. 6B, the respective elements are isolatedfrom each other by means of photolithography using RIE. After that, aSiN film serving as the protective film is deposited to a thickness ofabout 900 nm using a plasma CVD apparatus, and the SiN film is partiallyremoved by means of photolithography using RIE so that interconnectionpads or the like are exposed.

Thereafter, a fluorescent substance is bonded using an adhesive or thelike, and thus a major part of the X-ray detecting apparatus accordingto the present invention is obtained.

Second Embodiment

In the below described second embodiment, a FPD-type X-ray detectingapparatus using MIS-type optical-to-electrical converters as in thefirst embodiment is disclosed. Compared with the X-ray detectingapparatus according to the first embodiment, the sensitivity of theX-ray detecting apparatus according to the second embodiment is furtherimproved by increasing the aperture ratio, and the TFT driving circuitis simplified.

FIG. 7 is a circuit diagram showing an equivalent circuit of an X-raydetecting apparatus having a 3×3 matrix structure according to thepresent embodiment. Although the X-ray detecting apparatus has the 3×3matrix structure by way of example, the matrix structure may includegreater numbers of rows and columns. For convenience, similar parts tothose in the first embodiment are denoted by similar reference numeralsor symbols.

In FIG. 7, reference numeral 11 denotes an individual MIS-typeoptical-to-electrical converter, 12 denotes a transfer TFT, 13 denotes adriving line for driving the transfer TFT or reset TFT, 14 denotes asignal line, 15 denote a bias line, 16 denotes a signal processingcircuit, 17 denotes a TFT driving circuit, 18 denotes an A/D converter,19 denotes a reset TFT, and 21 denotes a resetting line.

Incident X-ray radiation is converted into visible light by a wavelengthconversion element such as a CsI or GOS, and the resultant visible lightis incident on the MIS-type photoelectric conversion element 11. Theincident light is converted into an electric charge by the MIS-typephotoelectric conversion element 11, and the resultant electric chargeis stored in the MIS-type photoelectric conversion element 11.Thereafter, the transfer TFT 12 of the current pixel is turned on toread the stored electric charge. The reset TFT 19 of the pixel is turnedon, in synchronization with the operation of the transfer TFT at thefollowing stage, thereby resetting the sensor.

FIG. 8 is a circuit diagram showing an equivalent circuit of an X-raydetecting apparatus having a 3×1 matrix structure. In this figure,similar parts to those in FIG. 7 are denoted by similar referencenumerals. When an on-voltage is applied to a transfer TFT TT1 via a nodeVgt(1), a signal is output via a line Sig. Thereafter, an on-voltage isapplied to a reset TFT TR1 via a node Vgr(1) to reset a sensor.Similarly, when an on-voltage is applied to a transfer TFT TT2 via anode Vg(t), a signal is output via the line Sig. Thereafter, anon-voltage is applied to a reset TFT TR2 via a node Vg(3) to reset asensor. By performing the above-described operation repeatedly, a movingimage is read.

FIG. 9 is a diagram showing a method of driving the X-ray detectingapparatus according to the present embodiment. In FIG. 9, referencesymbol S1 denotes a period of time needed to read one line, S2 denotes aperiod of time needed to reset one line, S4 denotes a period of timeneeded to accumulate an electric charge into a sensor, and S denotes aperiod of time needed to perform the entire process on one frame.

In the present embodiment, unlike the conventional method in whichsequential reading, and resetting and exposure to radiation for allpixels are performed repeatedly, reading, resetting, and storing areperformed on a line-by-line basis, and thus the total driving time issubstantially equal to the sum of reading times. That is, when readingand transferring of signals from pixels in one line are being performed,resetting of already-read pixels in a previous line is performed. Thismakes it possible to drive the X-ray detecting apparatus at a highdriving rate of 30 FPS or higher to obtain a moving image withoutcausing degradation in image quality.

FIG. 10 is a plan view showing one pixel of the X-ray detectingapparatus according to the present embodiment. In FIG. 10, similar partsto those in FIG. 7 are denoted by similar reference numerals. In FIG.10, the transfer TFT 12 and the reset TFT 19 are disposed in diagonallyopposite corners of the pixel in order to achieve an optimum layoutincluding the driving line and the signal line. In this structure, theon-time is the same for both the transfer TFT and the reset TFT, andthus it is not necessary required that the TFTs have the same drivingcapability, and the driving capability may be determined depending onthe driving method or the image quality required.

In the present embodiment, the number of lines for driving TFTs issimilar to that employed in the conventional technique, and it ispossible to drive the X-ray detecting apparatus at a high driving rateto obtain a moving image without needing a significant modification ofthe peripheral circuits. Furthermore, the X-ray detecting apparatusaccording to the present embodiment can be easily produced by a simplemethod similar to that employed in the first embodiment.

In the first and second embodiments described above, the MIS-typeoptical-to-electrical converter is employed by way of example as thephotoelectric conversion means. Alternatively, a PIN PD may be employedfor the same purpose.

Third Embodiment

In the below described third embodiment, a direct conversion techniquefor directly converting radiation to an electric charge, storing theobtained electric charge, and reading the electric charge using atransfer TFT is disclosed.

FIG. 11 is a circuit diagram showing an equivalent circuit of an X-raydetecting apparatus having a 3×3 matrix structure according to thepresent embodiment. Although the X-ray detecting apparatus has the 3×3matrix structure by way of example, the matrix structure may includegreater numbers of rows and columns.

In FIG. 11, reference numeral 32 denotes an individual electrode forcollecting an electric charge generated in the direct radiationconversion element, 30 denotes a storage capacitor, 22 denotes atransfer TFT, 23 denotes a driving line for driving the transfer TFT andthe reset TFT, 24 denotes a signal line, 26 denotes a signal processingcircuit, 27 denotes a TFT driving circuit, 28 denotes an A/D converter,29 denotes a reset TFT, and 31 denotes a resetting line.

FIG. 12 is a cross-sectional view showing a pixel and nearby portions ofthe X-ray detecting apparatus according to the present embodiment. InFIG. 12, reference numeral 41 denotes a glass substrate, 42 denotes adirect radiation conversion element made of amorphous selenium or GaAs,50 denotes a common electrode, and 32 denotes an individual electrode.Reference numeral 43 denotes a connection element in the form of a bumpmade of electrically conductive resin. 51 denotes a gate electrode ofthe transfer TFT or the reset TFT, 45, 46 and 47 denote a gateinsulating film, an active layer, and an ohmic contact layer,respectively, of the transfer TFT or the reset TFT, and 52 denotes alower electrode of the storage capacitor.

Incident X-ray radiation is converted by the direct radiation conversionelement 42 to an electric charge and collected into the individualelectrode 32. The collected electric charge is stored in the storagecapacitor 30 via the connection element in the form of the bump 43.Thereafter, the transfer TFT 22 is turned on to read the stored electriccharge via the signal line 24. After that, when the transfer TFT at thefollowing stage is turned on, the reset TFT 29 is turned on at the sametime, thereby resetting the sensor and the storage capacitor.

Also in the present embodiment, great advantages similar to thoseobtained in the first or second embodiment are obtained, and it ispossible to easily obtain a high-quality moving image.

Fourth Embodiment

Referring to a cross sectional view shown in FIG. 20, an radiationdetecting apparatus according to a fourth embodiment is described below.In this fourth embodiment, a MIS-type optical-to-electrical converter isformed on a transfer TFT and also on a reset TFT via a planarizing filminto a multilayer structure. In FIG. 20, reference numeral 41 denotes aninsulating substrate made of glass or the like, 61 denotes a gateelectrode of the transfer TFT, 62 denotes a gate electrode of the resetTFT, 45 denotes a gate insulating film, 46 denotes a semiconductorlayer, 47 denotes an ohmic contact layer, 63 denotes a planarizing film,64 denotes a first electrode layer of the optical-to-electricalconverter, 65 denotes an insulating layer, 66 denotes a semiconductorlayer, 67 denotes an ohmic contact layer, and 68 denotes a secondelectrode layer. The equivalent circuit of the X-ray detecting apparatushaving a 3×3 matrix structure according to the present embodiment issimilar to that shown in FIG. 1, and the equivalent circuit of the X-raydetecting apparatus having a 3×1 matrix structure according to thepresent embodiment is similar to that shown in FIG. 2.

In the X-ray detecting apparatus constructed in the above-describedmanner, because the optical-to-electric converters are formed on drivingelements such as TFTs into the multilayer structure, the aperture ratiois improved, and the driver circuit including TFTs is simplified. Inparticular, in the case in which the MIS-type optical-to-electricalconverter is used as the optical-to-electrical converter, after formingthe planarizing film 63, the contact hole is formed and the firstelectrode layer and the electrode of the TFT are connected to each othervia the contact hole, and thus the planarizing film makes it possible toreduce the thickness of the insulating film of the MIS-typeoptical-to-electrical converter thereby improving the sensitivity. Thus,this structure is especially desirable.

While the present invention has been described with reference to whatare presently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. On the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims it is beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

1. A radiation detecting apparatus comprising: a plurality of pixels,each pixel including (i) a conversion element configured to convertradiation into an electric signal, (ii) a resetting element configuredto reset said conversion element by applying a voltage to saidconversion element, and (iii) a signal transfer element connected tosaid conversion element, wherein said signal transfer element and saidresetting element are connected to the same electrode of said conversionelement, and wherein said conversion element is formed on said signaltransfer element and on said resetting element via a planarizing layer,and said same electrode is formed on said planarizing layer.
 2. Aradiation detecting apparatus according to claim 1, wherein said signaltransfer element and said resetting element are each formed of athin-film transistor.
 3. A radiation detecting apparatus according toclaim 1, wherein said signal transfer element and said resetting elementare connected to the same driving interconnection line.
 4. A radiationdetecting apparatus according to claim 1, wherein the pixels arearranged in an array having rows, and a transfer operation for a row isperformed by said signal transfer element in a period of time in whichsaid resetting element resets an immediately preceding row which hasbeen subjected to the transfer operation.
 5. A radiation detectingapparatus according to claim 4, wherein transfer elements of pixels in aspecific row and resetting elements of pixels in a previous row areconnected to the same driving line so as to simultaneously perform thetransfer operation by the first thin film transistors on the specificrow and the resetting operation by the resetting elements on theprevious row the transfer operation for which has been completedimmediately prior to starting the transfer operation for the specificrow.
 6. A radiation detecting apparatus according to claim 1, whereinsaid conversion element is formed of layers including an electrodelayer, an insulating layer, a semiconductor layer, and a carrierblocking layer such that said conversion element has the same layerstructure as said transfer element.
 7. (canceled)
 8. A radiationdetecting apparatus according to claim 1, wherein said conversionelement is formed of non-single crystal silicon.
 9. A radiationdetecting apparatus according to claim 1, further comprising awavelength conversion element of CsI or GOS for converting radiation tovisible light.
 10. A radiation detecting apparatus according to claim 1,wherein said conversion element includes a member for directlyconverting radiation to an electric charge.
 11. (canceled)
 12. Aradiation detecting apparatus comprising: an array of pixels having aplurality of rows, each pixel including (i) detection means fordetecting radiation, (ii) transfer means for transferring a detectedsignal, and (iii) resetting means for resetting said detection means byapplying a voltage to said detection means, wherein said transfer meansand said resetting means are connected to a same electrode of saiddetection means, and wherein said detection means is formed on saidtransfer means and on said resetting means via a planarizing layer, andsaid same electrode is formed on said planarizing layer.